Because of increasing concerns over the environmental impact of fluorocarbon refrigerants such as freons, and legal restrictions on their manufacture, sale, and use, reliable sources of refrigerants are increasingly difficult to find. One consequence of this fact is that refrigeration systems are frequently contaminated with mixtures of different refrigerants and/or other substances. Contamination of refrigeration systems is a serious problem for those service technicians responsible for repairing and maintaining these systems, and particularly for those who warrant their work. Prior to the present invention, when a complaint was made about repair or maintenance of a refrigeration system, a service technician could not determine whether or not the system had been tampered with subsequent to the servicing. Thus, some service technicians have had to honor warranty claims where the failure of the system was not due to the original servicing, but to subsequent tampering.